The MHD channel requires a fluid stream with a high temperature, passing at a high velocity through a static magnetic field and having a constituent of ionizable material. Part of the heat energy of the fluid stream is converted directly into electrical energy by an MHD generator. Additional heat energy of the fluid stream is converted into electrical energy by a vapor generator whose output is converted into electrical energy by a turbine coupled to an electrical generator. The efficiency of the conversion by the MHD generator and vapor generator can be as high as 50%.
The well-established problems of bringing combustion air up to about 2500 F. and supplying appropriate fuel to the MHD generator, are well known. The ionized components of the products of combustion are enhanced by the introduction of seed, usually a form of potassium such as K.sub.2 CO.sub.3 or KCO.sub.2 H. SO.sub.2 in the products of combustion will combine with these potassium compounds and form K.sub.2 SO.sub.4. Common accepted practice has been to apply one of several available chemical processes to extract the sulfur of K.sub.2 SO.sub.4, regenerate fresh potassium seed, and recycle this seed to the combustor. The sulfur compound level of the output gas has been thereby reduced toward acceptable environmental standards.
Seed in the form of K.sub.2 SO.sub.4 can also be used to ionize gases leaving the MHD combustor. Providing that this seed can be recovered downstream of the MHD diffuser, there remains the problem of lowering the SO.sub.2 level of the diffuser discharge after passage through the vapor generator receiving the channel output. If the SO.sub.2 level can be reduced without seed regeneration for reduction of K.sub.2 SO.sub.4, the system will be less complex to operate and will consume less auxiliary energy. The energy consumption of seed regeneration processes frequently has a significant effect on the conversion efficiency of the combined plant, and cost of electricity. Most seed regeneration processes are wet processes, involving dilute potassium solutions. The energy requirements to evaporate this water from the solutions can add substantial penalties to the plant. In addition, few of these processes have, to date, been successfully demonstrated.